My house is 10 years old. It has windows with plastic grids. The last couple of years I've noticed a chalky substance on the grids when I run my finger along them. When it rains hard, the chalky substance runs off of the grids and onto my windows. Even when I try to clean the windows, if the rag touches the grids accidently, it smears all over the glass. Does anybody know what this stuff is and how I can get rid of it? Thanks in advance.